An example of a known contactless liquid level sensor (for example, Patent Reference 1) will be described. FIG. 5 is a vertical cross-sectional view of a known contactless liquid level sensor. FIG. 6 is a perspective view showing the positional relation between a magnetic-electric conversion element, a magnet and a stator extracted from the contactless liquid level sensor shown in FIG. 5. FIG. 7 is an enlarged vertical cross-sectional view of a key point showing a known contactless liquid level sensor where a magnet chamber cover is attached to a magnet chamber.
As shown in FIG. 5, a known contactless liquid level sensor 100 is arranged so that a sensor housing 110 made of synthetic resin will be fixed in a vehicle fuel tank 190. In a magnet chamber 110A formed in the sensor housing 110 is rotatably arranged a rotary shaft 120. On the outer circumference surface of the rotary shaft 120 is fitted a sintered magnet 130. The sintered magnet 130 is fixed to the rotary shaft 120 via fixing means such as bonding or engagement.
The sintered magnet 130 is for example a ferrite magnet formed by annularly molding magnetic powder and radially magnetizing the resulting mold of magnetic powder to the two poles. The sintered magnet 130 is hard and brittle and will suffer from cracks in the process of insert molding described later. Thus, a main body part formed via insert molding is fixed to the rotary shaft 120 via fixing means such as bonding or engagement as described earlier.
As shown in FIG. 7, to the opening in the magnet chamber 110A is fixed a magnet chamber cover 111 made of synthetic resin by engaging a claw 110B formed on the sensor housing 110 and an engaging hole 111A provided in the magnet chamber cover 111. Further, the magnet chamber cover 111 has a support hole 111B formed therein. In the support hole 111B is inserted and rotatably supported one end of the rotary shaft 120.
As shown in FIG. 5, the other end of a float arm 150 one end of which is attached to a float 140 is fitted to the hole in the rotary shaft 120 and is integrally fixed to the rotary shaft 120. When the float 140 moves up and down with variations in the liquid level L, the vertical movement is transmitted to the rotary shaft 120 via the float arm 150 to rotate the rotary shaft 120.
As shown in FIG. 6, a stator 160 is composed of a pair of pieces in the shape of a substantial semi-circle and is arranged to form a substantial circle while opposed to the outer circumferential surface of the sintered magnet 130. Between both end surfaces of the pair of stators 160 is formed two gaps G, G having a phase difference of 180°. In one gap G is arranged, for example, a magnetic-electric conversion element 170 such as a Hall element or a Hall IC while sandwiched by a pair of stators 160. The terminal 170A of the magnetic-electric conversion element 170 is electrically connected to a wiring plate 180 shown in FIG. 5. To the wiring plate 180 is electrically connected a terminal 180A.
When the float 140 moves up and down with variations in the liquid level L, the rotary shaft 120 rotates together with the sintered magnet 130. When the magnetic flux density passing through the magnetic-electric conversion element 170 varies with the rotation of the sintered magnet 130, the magnetic-electric conversion element 170 detects the variation in the magnetic flux density and converts the variation to an electric signal and outputs the same to the terminal 180A.